Heretofore, there is known a TIG welding process for supplying a filler wire to a space to generate an arc therein between a TIG torch and a workpiece, thereby forming a bead on a surface of the workpiece.
For example, motorcycle frames include a thin workpiece and a thick workpiece, which are made of aluminum or aluminum alloy, that overlap each other to provide a weld region. Then, a TIG welding process is performed on the weld region to form a scale-like bead in the weld region, joining the two workpieces.
The TIG welding process for the two workpieces requires much more heat energy to be consumed than a process of welding workpieces made of iron or the like.
The motorcycle frames are disposed in positions which attract public attention. Therefore, the quality of the scale-like bead governs the customer attraction capability of the motorcycle frames.
For this reason, the motorcycle frames are TIG-welded by skilled technicians of the TIG welding process.
It is not easy to hand down the TIG welding techniques from the skilled technicians to general welding technicians. Further, it is difficult to increase the production efficiency of motorcycle frames even when the skilled technicians perform the TIG welding process.
Attempts have been made to cause an articulated robot to perform the TIG welding process which has been performed by the skilled technicians, thus increasing the frame production efficiency.
In such an articulated robot, a TIG torch and a filler wire guide are held by an arm of the articulated robot, and a filler wire is supplied from the filler wire guide to a space defined between the TIG torch and a weld region of two workpieces. The TIG torch is oscillated in a weaving action for performing a TIG welding process.
However, when the TIG torch makes a weaving action, a position of the TIG torch and a position of the filler wire with respect to the surfaces of the two workpieces vary. Therefore, the amount of the filler wire which is required to form the bead varies. Therefore, when the bead is formed, the state of the molten well of the filler wire that is formed in the weld region becomes unstable, forming a faulty bead. The faulty bead reduces the customer attraction capability of the motorcycles.